1. Field of Invention
The present invention pertains to downhole flow control devices, and particularly to downhole flow control devices using a common control line as a pressure source for operation.
2. Related Art
In running intelligent completions into subterranean wells, there are often limitations on the number of control line penetrations that can be made at the wellhead, the tubing hanger, or, in some cases, the production packer.
Intelligent completions use various means to regulate flow control devices placed downhole to control production from various zones. Such flow control devices, valves, for example, can typically be fully open, partially open (choked), or fully closed. Using a plurality of such valves allows an operator to selectively receive or restrict production from different zones. A simple version of such a flow control device would typically have two control lines, one acting on either side of a piston. When multiple valves of that kind are run in the hole, the number of control lines required becomes a problem. For example, three valves would require six control lines.
There also exist single control line flow control devices that rely on energy stored in the downhole device, such as a charge of compressed gas (e.g., nitrogen spring) or a mechanical spring working in conjunction with either the annular or tubing pressure. Since downhole conditions may change over time, selection of the spring or nitrogen charge is critical and may limit the operational envelope of the flow control device. Various multiplexing schemes have been employed, but those typically require some complex scheme of valves to allow pressures at different levels to address one valve or another. A common return line has been proposed for simple, two position-type valves (i.e., open/close valves), but operation can be tricky as one must carefully assess the state of each valve to determine the proper pressure sequence to apply to the various control lines at surface.